5 Stage under sink PA-E RO 132, reverse osmosis water systems include three vertical pre-filters that must be replaced periodically. 
The filters represent the different stages the water goes through while being purified.Generally, Pre-Filters and Post-Filters in the PA-E RO 132 water systems can last around 8 To 12 months between changes. 
 
        Stage 1 - Pre-Membrane reverse osmosis sediment filters
Replacement High-Grade 5-micron high-capacity  sediment filter 
Remove larger particles & suspended matter such as dirt, silt, rust, and sand from water.   
Protects and extends the life of the membrane and system.
Recommend replacement every 8 -12 months, varies depending on the water source quality   
Standard Size  water filters 10.2" x 2.5"
Stage (1) Pre-Membrane
 
            Stage 2- Organic Activated Carbon GAC filter 
They are well-known for their highly efficient reduction of chlorine taste, odor taste, and odors of many organic chemicals and volatile organic compounds.
All GAC filters are made with Organic, high-quality coconut shell carbon. This filter is wrapped and sealed and meets NSF Standards and Regulations. The filter will fit any Residential Reverse Osmosis Unit with standard 10” filter housing. Micron rating: 5 Micron.
Dimensions: 10" x 2.5"
Lifetime: Replace every year, depending on the water quality.
Stage (2) Pre-Membrane
    
          Stage 3- CTO Coconut Shell Carbon Block Filter 
Organic CTO Coconut Shell Carbon Block Filter
Forceful removal of pesticide residues in water, water pollution odor of ozone, chlorine removal of residual heavy metals, bacteria, sterilization rate if 99%.
Standard Size  10" x 2.5"
Recommend replacement every 8 To 12 months.
Protects and extends the life of the membrane and system.
Stage (3) Pre-Membrane.